Despite numerous attempts at making better solar cells with new and exotic materials, the photovoltaics market is still dominated by early or first generation solar cells that are typically silicon wafer-based solar cells. Most solar cell manufacturers are equipped to produce silicon wafer-based solar cells, and research continues to design silicon-based solar cells that can achieve higher conversion efficiencies without an exorbitant increase in production costs, e.g., the aim of research often is to achieve the lowest cost per watt solar cell design that is suitable for commercial production. In addition to use in solar cells, silicon wafers, other silicon layers on substrates, and objects having silicon surfaces are used in numerous other applications such as in electronic devices, telecommunication devices, computers, and even in biological or medical applications. These other applications have also driven research to methods of fabricating silicon wafers and silicon surfaces with particular qualities or characteristics such as a rough, textured, or nanostructured surface.
The performance of solar cells and other optoelectronic devices is directly related to optical losses caused by high reflectivity. Flat silicon surfaces such as those found on an untreated silicon wafer have a high natural reflectivity across the entire range of the solar spectrum that results in losses of light that could otherwise be converted to electrical energy by the silicon photovoltaic device. To produce high efficiency solar cells, researchers have sought ways to minimize reflection losses.
While etching processes produce highly non-reflective or “black” silicon surfaces, there are a number of drawbacks that may hinder wide adoption of such processes. A silicon device with a black silicon surface or region is useful because it is rough or fuzzy to a depth of about a wavelength of light, but this irregular, porous region has a large amount of surface area when compared with a flat or planar silicon surface. Generally, in solar cells and some other applications, large amounts of surface area are considered undesirable as it may result in loss of photogenerated minority carriers that leads to a reduction in light detection efficiency or energy conversion efficiency. Stated another way, the use of black silicon or density graded layers or regions to control reflection does not make sense in terms of dollar-per-Watt unless high energy conversion efficiency can be achieved. Accordingly, it would still be desirable to develop techniques that allow the large, irregular surface area of the black silicon to be passivated (e.g., to provide surface passivation) that do not significantly increase manufacturing complexity, fabrication times, and material or other manufacturing costs for high-efficiency silicon solar cells, detectors, and other devices.
The foregoing examples of the related art and limitations related therewith are intended to be illustrative and not exclusive. Other limitations of the related art will become apparent to those of skill in the art upon a reading of the specification and a study of the drawings.